feat: Add chat handler with RAG pipeline

- chat_handler.py: Standalone NATS handler with RAG
- chat_handler_v2.py: Handler-base implementation
- Dockerfiles for both versions

Pipeline: Embeddings → Milvus → Rerank → LLM → (optional TTS)

requirements.txt

@@ -0,0 +1,15 @@
+nats-py
+httpx
+pymilvus
+numpy
+msgpack
+redis>=5.0.0
+opentelemetry-api
+opentelemetry-sdk
+opentelemetry-exporter-otlp-proto-grpc
+opentelemetry-exporter-otlp-proto-http
+opentelemetry-instrumentation-httpx
+opentelemetry-instrumentation-logging
+# MLflow for inference metrics tracking
+mlflow>=2.10.0
+psycopg2-binary>=2.9.0